The IEEE802.16-based Wireless Metropolitan Area Network (WiMAX) provides a wireless access solution for wideband access service, and the WiMAX standards adopts an Orthogonal Frequency Division Multiple Access (OFDMA) technology. But its coverage is limited by power and transmission technique, especially in metropolitan areas. At the edge of a cell or in regions which are shadowed, data throughput of a user drops dramatically and complex wireless environment may also result in coverage blind areas. In view of the above problems, the solution of simply increasing the density of base stations will only result in increase of facilities and network wiring costs.
Therefore, there is provided a wireless access system with a lower cost, comprising a mobile station, a base station, and a relay station for receiving and forwarding message between the mobile station and the base station under the base station control. After the relay capability is integrated into a wireless access network system, the system may expand coverage and enhance data throughput.
However, in the current wireless access system, there is not specified a method of how to implement roaming handover control. It is well known that handover control is an important issue in the wireless access technology. To expand coverage, the relay station must supports roaming and handover of the mobile station. The handover includes handover of the mobile station between the base station and the relay station as well as between a relay station and another relay station, and handover of the mobile station cross base stations. The mobility of the relay station per se is also an important issue
In view of the above problems, a feasible solution for handover control in a mobile multi-hop relay wireless access system is desired.